Power apparatus for truck loading elevator

ABSTRACT

A dock lift has a platform connected at each side to a frame by a scissors apparatus. At one end, a pair of crossed hydraulic cylinders connect the platform and the frame. The hydraulic connections to the cylinders are made so that a load imposed on one side of the platform imposes a load on one cylinder which cylinder in turn causes fluid pressure to be applied to the other cylinder in the sense such that the other side of the platform is drawn downwardly to aid in maintaining the platform approximately level.

SUMMARY OF THE INVENTION

The present invention relates to a hydraulically operated dock lifthaving features to increase the stability of the platform and aid inmaking the conditions under which employees use the dock lift more safe.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is a side elevational view of the embodiment of FIG. 1 with theplatform raised;

FIG. 3 is an end view with the platform lowered and a cover plateremoved; and

FIG. 4 is a schematic diagram of the power apparatus for the hydrauliccylinders.

DESCRIPTION OF THE SPECIFIC EMBODIMENT

The following disclosure is offered for public dissemination in returnfor the grant of a patent. Although it is detailed to ensure adequacyand aid understanding, this is not intended to prejudice that purpose ofa patent which is to cover each new inventive concept therein no matterhow others may later disguise it by variations in form or additions orfurther improvements.

In the illustrated embodiment there is a base or frame, generally 10,above which is a platform, generally 11. At each side, the base andplatform are connected by a scissors apparatus, generally 12. Each ofthese scissors apparatus comprises two levers 13 and 14. At one end thelevers are pivotally connected to the platform and the baserespectively, the pivot pins being designated 15 and 16. The other endsof the levers have wheels 17 and 18 which respectively bear on the baseand platform. Adjacent one end, hydraulic power means, generally 19,interconnect the base and platform. A removable and dirigible wheel 20can be mounted at one end of the base. Provision is also made at theother end of the base to selectively support the base on wheel structureso that it may be moved about. The platform is provided with dock boards21 and a guard rail 22. As thus far described in this paragraph, theapparatus is conventional. The illustrated wheel structure, generally23, on the base in opposition to dirigible wheel 20 is the subjectmatter of a copending application entitled Wheel Activator ForAmbulatory Truck Loading Elevator, SN 331,640, filed Feb. 12, 1973 nowU.S. Pat. No. 3,806,092 also being my invention.

In the disclosed embodiment the hydraulic power means 19 comprises apair of hydraulic cylinders 27 and 28 respectively. Hydraulic cylinder27 has a clevis 29 on its closed end, which clevis is pivotallyconnected by a pin 30 to the base 10. Similarly, a clevis 31 and pin 32connect the closed end of cylinder 28 to the base 10. Extending from theopen end of the cylinders are rams or piston rods 33 and 34 respectivelywith suitable seals between the piston rod and the wall of the cylinderat the open end. The piston rods are secured to pistons 35 and 36 (FIG.4) within the cylinders.

A deck 38 and box-like enclosure 39 at one end of the deck form astructural part of platform 11. This enclosure has an open bottom 40.One side is formed by a removable panel or cover plate 41. At the topinside corners of the box are two gussets 42 and 43. At the distal endof piston rod 34 is a clevis 44 and at the top end of piston rod 33 is aclevis 45. These clevises are connected to gussets 42 and 43 by pins 46and 47 respectively. The box enclosure 39 also may be employed to housethe hydraulic pump with its motor, sump, etc. The hydraulic apparatus isschematically illustrated in FIG. 4. It comprises a hydraulic pump 50which is driven by an electric motor 51. The motor is energized from asuitable source of electricity through a normally open switch 52. Thepump draws hydraulic fluid 53 from a sump 54 through an intake line 55having a filter 56 therein. The hydraulic fluid is delivered underpressure to a fluid supply line 57. Extending from supply line 57 tosump 54 is a return line 58 having a pressure relief valve 59 therein.

A first cylinder conduit 62 communicates with cylinder 27 adjacent thepiston rod end thereof and with the hydraulic cylinder 28 at the closedend thereof. A second conduit 63 communicates with cylinder 27 at theclosed end thereof and with cylinder 28 adjacent the piston rod endthereof. There is a fluid discharge line 64 that communicates with sump54'. In actual practice, sumps 54 and 54' are a common sump orreservoir. In discharge line 64 is a flow control restriction 65 and anormally closed valve 66 operated by a solenoid 67. An electricalcircuit including a normally open switch 68 connects to solenoid 67. Byclosing switch 68 solenoid 67 is energized to open valve 66.

A first check valve 70 connects supply line 57 and conduit 62 to permitthe flow of hydraulic fluid only from the supply line to the conduit. Asecond check valve 71 connects supply line 57 with second conduit 63 topermit fluid flow only from the supply line to the conduit. A thirdcheck valve 72 connects first conduit 62 with discharge line 64 topermit fluid flow only from the conduit to the discharge line. A fourthcheck valve 73 connects second conduit 63 with discharge line 64 topermit fluid flow only from the conduit to the discharge line.

If the platform is to be raised from the lowered position (illustratedin FIG. 3) switch 52 is closed. This energizes motor 51 so that pump 50supplies hydraulic fluid under pressure to supply line 57. Thishydraulic fluid flows through check valves 70 and 71 to the bottom ofthe hydraulic cylinders and simultaneously to the tops of the hydrauliccylinders. However, since the bottom areas of pistons 35 and 36 aregreater than the top exposed area of the two pistons (the top exposedareas being diminished by the presence of piston rods 33 and 34), theforces applied to the bottoms of the pistons is greater than that on thetops. Therefore, the pistons will move toward the upper ends of thecylinders. Thus, the piston rods move outwardly from the cylinder andthe platform is thereby raised (the raised position being illustrated inFIG. 1).

When the desired elevation of the platform is achieved, switch 52 isreleased so that it automatically opens. Motor 51 and pump 50 stop. Whenit is desired to lower the platform, switch 68 is closed. This energizessolenoid 67 and opens valve 66 to permit fluid to flow from thecylinders through the two check valves 72 and 73 and the return line 64to sump 54'. The rate of flow is dictated by the restriction 65. Thus,the platform 11 descends at the desired speed. Once set, normally theflow control 65 is not changed. The rate of descension will not changeat any point along the path of movement of the platform.

Assume that platform 11 has an unbalanced load applied to it, theunbalanced load being such that it is greater at the right side asviewed in FIG. 3, that is, at the near side as viewed in FIG. 1. Thisuneven load therefore tends to push down on piston rod 33 to a greaterextent than it does on piston rod 34. Thus, the pressure on piston rod34 tends to compress the fluid below piston 36. Through conduit 62 thatfluid is applied to the top end of cylinder 27 and acts to apply adownward force to piston 35. At the same time, the same force applied topiston rod 34 tends to reduce the fluid pressure above piston 36.Through conduit 63 this reduction is communicated to the bottom end ofcylinder 27 and again results in the tendency of the piston 35 to movedownwardly. Thus the unbalanced, greater load applied to the cylinderattached to one side of the platform acts, through the hydrauliccircuit, to apply a compensating force to the hydraulic cylinderattached to the other side of the platform. The conduits 62 and 63 atthis time are blocked by check valves 70 and 71 and the closed valve 66.

If, as was the more common connection of two cooperating hydrauliccylinders, the bottom ends of the two cylinders were connected togetherto a common conduit and the top ends of the two cylinders were connectedtogether to a second conduit, the action would be self-defeating ratherthan cooperating. That is, the pressure applied to one side of theplatform would push down on the cylinder at that side of the platform.In turn, this would apply a fluid pressure to the bottom of the cylinderat the other side of the platform so that the other side of the platformwould tend to go up. Thus the loading of one side actually would tend tocause more tipping of the platform, rather than less as is the case withthe present invention.

Another important feature of the present invention is the use of thecrossed hydraulic cylinders. This gives a lower overall height (whetherthe platform is raised or lowered), a feature that is often veryimportant to dock lifts and the like, particularly ambulatory lifts. Itprovides a sway control against the platform moving from side to side toan extent that cannot be achieved by vertically positioned cylinders.This also enables the use of a single stage cylinder rather thanmultiple stage cylinders (two or more cavities and pistons therein). Itis extremely difficult to obtain a constant rate of movement withmulti-stage cylinders. An uneven movement in a lift or elevator is quiteundesirable.

Some of the dock lifts presently in commercial use employ two verticallypositioned hydraulic cylinders at one end of the platform. Thesecylinders are secured to the frame at the bottom while the top of thepiston rod has a gear over which extends a chain connected at one end tothe platform and the other end to the base. As compared to this type ofunit, the embodiments of the present invention are extremely maintenancefree and much less dangerous to employees who are using the lifts. Allof the undesirabilities of the chain are eliminated. In addition, theupper end of the cylinders and exposed piston rods are enclosed byenclosure or housing 39 which also serves to enclose the motor, pump,valves, etc. By providing a suitable locking device 75, damage to, andpilferage of, such items can be guarded against. Without being able tooperate the locking device 75 the panel 41 cannot be removed to obtainaccess to these items.

I claim: .[.1. In an apparatus such as a dock lift or the like and foruse with a source of hydraulic fluid under pressure, said apparatuscomprising a frame having two sides and two ends, a vertically movableplatform device above the frame and also having two corresponding sidesand two corresponding ends, two pair of scissors means respectivelyconnecting opposite sides of the frame and platform device, and powermeans at one end of the frame and connecting the frame and platformdevice for vertically moving the platform device with respect to theframe, the improvement comprising:.]. on the other side of theplatform..].
 2. In an apparatus as set forth in claim .[.1.]..Iadd.8.Iaddend., wherein the members attached to the piston rods aresecured to the platform device, and said hydraulic cylinders each are asingle stage
 3. In an apparatus as set forth in claim .[.1.]..Iadd.8.Iaddend.. wherein said platform device includes a deck with anenclosure at said one end of the device and extending above the level ofthe deck, said enclosure extending between said sides and having a topand an open bottom, said hydraulic cylinders extending into saidenclosure through said open bottom, the piston rod members beingattached adjacent said top immediately adjacent the respective
 4. In anapparatus as set forth in claim .[.1.]. .Iadd.8.Iaddend., wherein saidpower means includes a fluid supply line, a fluid discharge line, andfour check valves, one check valve being between the supply line and thefirst conduit to permit flow only in the direction toward the firstconduit, the second check valve being between the supply line and thesecond conduit to permit flow only in the direction toward the secondconduit, the third check valve being between the first conduit and thedischarge line to permit flow only in the direction toward the dischargeline, the fourth check valve being between the second conduit and thedischarge line to permit flow only in the direction toward the dischargeline, and a manually operable valve means in said discharge line tocontrol the fluid flow therethrough
 5. In an apparatus as set forth inclaim .[.1.]. .Iadd.4.Iaddend., wherein the source of hydraulic fluid isa fluid pump driven by an electric motor, said pump supplying fluid tosaid first and second check valves without the presence of anaccumulator therebetween; andincluding control means connected to saidmotor to energize and deenergize the same; whereby said platform israised only by operating said control means to energize said motor..[.6. In an apparatus such as a dock lift or the like comprising a framehaving two sides and two ends, a vertically movable platform deviceabove the frame and also having two corresponding sides and twocorresponding ends, two pair of scissors means respectively connectingopposite sides of the frame and platform device, and power means at oneend of the frame and connecting the frame and platform device forvertically moving the platform device with respect to the frame, and foruse with a source of hydraulic fluid under pressure, the improvementwherein said power means comprises:.]. .[.two hydraulic cylinders eachhaving a closed end, a piston rod extending from the other end, a firsthydraulic connection adjacent the closed end thereof, and a secondhydraulic connection adjacent the other end thereof;.]. .[.two hydraulicfluid conduits, one of said conduits communicating with the firstconnection of one cylinder and the second connection of the othercylinder to provide fluid communication therebetween, the other of saidconduits communicating with the second connection of said one cylinderand the first connection of said other cylinder to provide fluidcommunication therebetween;.]. .[.whereby a load imposed on saidplatform at a first side thereof will push down on the hydrauliccylinder connected to said first side of the platform which hydrauliccylinder will in turn act through the respective communication toenergize the other hydraulic cylinder to apply a downward pulling forceon the other side of the platform..].
 7. In an apparatus as set forth inclaim .[.6.]. .Iadd.9.Iaddend., wherein said power means includes afluid supply line and a fluid discharge line, and four check valves, onecheck valve being between the supply line and the first conduit topermit flow only in the direction toward the first conduit, the secondcheck valve being between the supply line and the second conduit topermit flow only in the direction toward the second conduit, the thirdcheck valve being between the first conduit and the discharge line topermit flow only in the direction toward the discharge line, the fourthcheck valve being between the second conduit and the discharge line topermit flow only in the direction toward the discharge line, and amanually operable valve means in said discharge line to control thefluid flow therethrough. .Iadd.
 8. In an apparatus such as a dock liftor the like and for use with a source of hydraulic fluid under pressure,said apparatus comprising a frame having two sides and two ends, avertically movable platform device above the frame and also having twocorresponding sides and two corresponding ends, two pair of scissorsmeans respectively connecting opposite sides of the frame and platformdevice, and power means at one end of the frame and connecting the frameand platform device for vertically moving the platform device withrespect to the frame, the improvement comprising:said power meanscomprising two hydraulic cylinders each cylinder having a closed end, apiston rod extending from the other end of the cylinder and connectingmembers on the closed end and the distal end of the piston rod, one ofsaid cylinders having one member thereof pivotally secured to the frameat one side and the second member thereof pivotally secured to theplatform device at the other side, the other of said cylinders havingone member thereof pivotally secured to the frame at said other side andthe second member thereof pivotally secured to the platform device atsaid one side, each cylinder having a first hydraulic connectionadjacent the closed end thereof and a second hydraulic connectionadjacent the other end thereof, said power means including two hydraulicfluid conduits, one of said conduits communicating with the firstconnection of one cylinder and the second connection of the othercylinder to provide fluid communication therebetween, the other of saidconduits communicating with the second connection of said one cylinderand the first connection of said other cylinder to provide fluidcommunication therebetween, fluid supply line means through whichhydraulic fluid flows from said source when said platform device is tobe raised and through which hydraulic fluid returns from said cylinderswhen said platform device is to be lowered, and means connecting thefluid supply line means and said conduits for preventing hydraulic fluidfrom flowing from said one of said conduits to said other of saidconduits when the platform device is not being raised or lowered,whereby a load imposed on said platform at a first side thereof willpush down on the hydraulic cylinder connected to said first side of theplatform which hydraulic cylinder will in turn act through therespective communication to energize the other hydraulic cylinder toapply a downward pulling force on the other side of the platform..Iaddend. .Iadd.
 9. In an apparatus such as a dock lift or the likecomprising a frame having two sides and two ends, a vertically movableplatform device above the frame and also having two corresponding sidesand two corresponding ends, two pair of scissors means respectivelyconnecting opposite sides of the frame and platform device, and powermeans at one end of the frame and connecting the frame and platformdevice for vertically moving the platform device with respect to theframe, and for use with a source of hydraulic fluid under pressure, theimprovement wherein said power means comprises: two hydraulic cylinderseach having a closed end, a piston rod extending from the other end, afirst hydraulic connection adjacent the closed end thereof, and a secondhydraulic connection adjacent the other end thereof; two hydraulic fluidconduits, one of said conduits communicating with the first connectionof one cylinder and the second connection of the other cylinder toprovide fluid communication therebetween, the other of said conduitscommunicating with the second connection of said one cylinder and thefirst connection of said other cylinder to provide fluid communicationtherebetween; fluid supply line means through which hydraulic fluidflows from said source when said platform device is to be raised andthrough which hydraulic fluid returns from said cylinders when saidplatform device is to be lowered; and means connecting the fluid supplyline means and said conduits for preventing hydraulic fluid from flowingfrom said one of said conduits to said other of said conduits when theplatform device is not being raised or lowered; whereby a load imposedon said platform at a first side thereof will push down on the hydrauliccylinder connected to said first side of the platform which hydrauliccylinder will in turn act through the respective communication toenergize the other hydraulic cylinder to apply a downward pulling forceon the other side of the platform..Iaddend.